1. Field of the Invention
The present invention relates to a method and an apparatus using laser induced breakdown spectroscopy (xe2x80x9cLIBSxe2x80x9d) to identify a constituent in a process to produce a soot and to determine the amount of the constituent. More specifically, the present invention relates to a method and an apparatus using photon emissions to identify the constituent and to determine the amount of the constituent in a soot formed from a chemical vapor deposition (xe2x80x9cCVDxe2x80x9d) process to produce a product such as an optical waveguide fiber (xe2x80x9coptical fiberxe2x80x9d). The invention may also be used to identify a constituent and its concentration level in a flame of a deposition burner for applying the soot to a substrate. The invention may further be used to determine a constituent and its concentration in a reaction stream or on a solid surface.
2. Technical Background
In a CVD process, a particulate is formed and deposited on a substrate. CVD processes may be used in the manufacturing of various products. CVD techniques may be used to apply coatings to glazings as well as other types of substrates. CVD technology may also be used to form glass articles such as photolithography lenses, optical fibers, and photonic amplifiers.
The optical fiber typically includes a cladding made of pure silica (SiO2) and a core made of silica doped with germanium dioxide (GeO2) or some other index of refraction modifying dopant. The dopant alters the refractive index of the silica in the core or cladding creating structures to funnel light. Portions of the core often contain different concentrations of germanium, fluorine, phosphorus, titanium oxide, or other dopants, resulting in different refractive indexes along the diameter of the core. The distribution of refractive indexes along the diameter of the core (i.e., the refractive-index profile) determines operating characteristics of the optical fiber.
A conventional process known as outside vapor deposition (xe2x80x9cOVDxe2x80x9d) can be used to form the optical fiber. Generally, the OVD process involves forming a soot preform by burning a gaseous mixture to produce soot containing silica and at least one dopant, such as germanium dioxide. Layers of the soot are successively deposited onto a mandrel to form a core portion of the soot preform.
A cladding is formed on the core portion by burning a gaseous mixture to produce soot containing silica and index reducing or increasing dopants, and successively depositing layers of that soot onto the core portion. The soot preform is consolidated by sintering the preform to form a glass blank. An optical fiber is drawn from the glass blank. The concentrations of dopant in the soot layers forming the fiber primarily determine the concentrations of dopant along the diameter of the resulting optical fiber.
It would be desirable to measure the concentrations of the dopant in the soot layers to determine if the soot preform can be expected to produce an optical fiber with a desired refractive-index profile. Currently, the concentration of the dopant of the soot preform is measured off-line. The off-line process is typically expensive and time consuming. Off-line processes also include many handling steps, which may introduce a significant source of contamination, loss of product, and/or sampling errors. Also, off-line measurements cannot be used to control on-line processing.
Also, controlling the refractive index profile of the optical waveguide fiber is mandatory for commercial fiber designs. This is especially the case for complex refractive index profile fibers. The traditional manufacturing processes of producing optical fiber have new challenges in terms of the precision requirements of the deposition of the soot, the consolidation, and the draw. An on-line method, which could identify the constituents in the preform, either the dopants or the silica, and also determine the concentration of each constituent is desired.
One aspect of the present invention includes a method of determining the identity of a constituent and/or its concentration level in a soot deposited on a soot coated substrate. The method includes the steps of sending a pulse of energy toward the coated substrate, focusing the energy to a predetermined point on the substrate to thereby generate a plasma on the substrate and to create at least one photon, detecting the photon using an analysis element, and identifying the constituent or its amount in the soot.
Another aspect of the invention includes a method for determining the identity and/or concentration of at least one reactant in the flame of a chemical vapor deposition process for depositing a soot on a substrate. The method includes the steps of sending a pulse of energy toward the flame, focusing the energy to a predetermined point in the flame to thereby generate a plasma in the flame and to create at least one photon, detecting the photon using an analysis element, and identifying the constituent or its amount in the flame.
A further aspect of the invention includes a method of controlling the manufacture of the soot deposited on the substrate. The method includes the steps of sending a pulse of energy toward a substrate, focusing the energy to a predetermined point on the substrate to thereby generate a plasma on the substrate and to create at least one photon, detecting the photon using an analysis element, and determining the identity or amount of the constituent in the soot, comparing the identity or amount of the constituent to a predetermined set of parameters, and adjusting at least one reaction condition such that the identity or amount of the constituent will be altered to match at least one of the predetermined set of parameters.
An additional aspect of the invention includes a soot coated substrate made from a process comprising the steps of depositing a soot on a substrate, sending a pulse of energy toward the coated substrate, focusing the energy to a predetermined point on the substrate to thereby generate a plasma on the substrate and to create at least one photon, detecting the photon using an analysis element, and determining the identity on amount of the constituent in the soot.
Yet another aspect of the present invention includes a method for determining the diameter or thickness of the substrate. The method includes the steps of sending a pulse of energy toward a substrate, focusing the energy to a predetermined point on the substrate to thereby generate a plasma on the substrate and to create at least one photon, detecting the photon using an analysis element, identifying the constituent and its amount in the soot, and measuring the thickness of the substrate.
An additional aspect of this invention may include utilizing the laser induced breakdown spectroscopy technique of using a laser to create a plasma and thereby generate photons to identify elements and their concentrations. This may be incorporated into the method of determining the identity of at least one constituent in the soot deposited on a coated substrate. In yet a further aspect of the invention, the coated substrate may be a precursor element for the production of an optical fiber.
The method of the invention results in a number of advantages over known techniques. The invention facilitates identifying the material deposited on the substrate, as well as, the concentration of the deposited material during the CVD process. This is the first time that the material deposited on a substrate and its concentration are able to be determined during depositing. This invention enables the CVD process to be integrated into a closed-loop control process. The invention also includes the advantage of determining the thickness of the substrate as well as the thickness of each layer of soot deposited on the substrate. The invention also has the advantage of a virtually non-contact measurement method so that significant perturbations to the CVD process are not generated by contact of the measurement device with the substrate during deposition. This may also be known as an untouchable measurement method. The invention has particular advantage for use in the closed-loop control system to more precisely manufacture a percursor element to produce an optical fiber.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.